Apparatus for extrusion



Nov 30, 1943. H M, GERSMAN 2,335,590

APPARATUS FOR EXTRUSION Filed Oct. 4, 1959 6 Shets-Sheet l INVENTOR HARVEY M. GEES/1AM @Awzmm% ATTORNE H. M. GERSMAN 2,335,590

' APPARATUS FOR EXTRUSION Nov 39, 1943.

6 Sheets-Sheet 2 Filed Oqt. 4, 1939 4m LAYER IN VENT OR HARVEY M GERSMAN ATTORN Q 1943 H. M. GERSMAN 2,3355% APPARATUS FOR EXTRUSION Filed 00L 4, 1939 6 Sheets-Sheet 3 (A) (B) (C) (D) (E) INVENTOR" F 19 HARVEY/1 GERSMAN Nov. 30, 1943. H. M. GERSMAN 2,335,590

APPARATUS FOR EXTRUSION Filed Oct. 4, 1939 6 Sheets-Sheet 4 v INVENTOR. HARVEY GERSMAN ATTORNE Fig, 16.

NVENTOR. HARVEY/1GER5M Nov. 30, 1943,

H. M. GERSMAN 2,335,590

APPARATUS FOR EXTRUSION 6 Sheets-Sheet 6 Filed 001;. 4, 1959 INVENTOR. HARVEY GERSMAN ATTORN Patented Nov. 30, 1943 UNITED STATES PATENT AOFFICE APPARATUS FOR EX'I'BUSION Harvey M. Gersman, New York, N. Y., assiglror to Ferrex Corporation, New York, N. Y., a corporation of Delaware Application October 4, 1939, Serial No. 297,920 16 Claims. (01. 207-17) This-invention relates to the art of extrusion and is particularly directed to an improved die and ram construction and to a method of extruprovided with an orifice of the contour desired in the finished article. This method of extrusion has produced fair results in the handling of ma-, terials possessed of considered plasticity.

In the handling of materials which are resistant to extrusion, however, such old methods have resulted in rapid destruction of the dies, particularly with the harder metals, together with the necessity of employing a large amount of power in operating the ram. Furthermore, because the material was merely pushed through an orifice with no regard for its natural flow, the physical characteristics of the extruded article were often had. In extruding many materials the old methods often produced an article with such poor physical characteristics that its only use was for ornamental purposes where little or no strength was required.

There have been attempts to provide a more efilcient extrusion process by giving various shapes to the work engaging surface of the die or ram, or both. Such designs have, insofar as I can determine, been predicated upon hypotheses which are at a variance with the basis of the present application and which hypotheses, I believe, are incorrect. Such shaping of the parts has possibly increased the extrusion eiliciency but this improvement has been very slight compared with the benefits obtained by my invention.

My extrusion process and the apparatus employed therein is adapted for use with a wide variety of materials. Steel, wrought iron, stainless steel, nickel and brass have, for instance, been satisfactorily extruded with my invention, and I contemplate its use in handling a variety 'of different materials, including plastics as well as metals. My invention finds its most important place in the extrusion of materials with a relatively low coeflicient of plasticity, that is, materials not easily pushed out of shape. Thus I find it commercially possible to extrude such materials as set out above.

The general object of my invention has been to provide an improved extrusion process and apparatus for using the process which will result in a markedly improved product with physical characteristics comparable to those obtained by otherwise working the same materials. Still another object of my invention has been to eliminate the die wear heretofore present and the corresponding wear on the ram. An additional object has been to extrude various materials, as metals, ceramics, plastics and the like along their natural flow lines with a corresponding decrease in the amount of power required and the consequent attaining ofthe improved product above named.

Plastic material, when placed in a die and pushed through an orifice, tends to assume natural lines of flow as it passes toward .and through the orifice. By correctly interpreting these lines of flow it is possible to provide an extrusion die and ram in which, with a-minimum of power, a maximum of extrusion efficiency can be obtained. I have found for instance that with apparatus constructed in accordance with my invention I 'can decrease, by approximately one-half, the

power applied to the ram in :handling a given shape.

An extruded article may be considered as made up of a series of concentric shells, each having a definite shell head and side walls extending from within the die out into the extruded article itself. The configuration and the thickness of the respective shells are determined by the configuration of the extrusion ram and die. I believe that the ram almost entirely controls the shape of the shell heads. The transverse spacing of these shells controls the hysical characteristics of the final product an thus is an indication of the degree of working to which the material is subjected in passing through the orifice. In articles to be subject to torsion the ram causes the flow which most thoroughly works the outer portion. The other extreme is to more thoroughly work the central portion. Any structure between the two extremes can be obtained as hereafter set out by properly controlling the material flow.

'The speed of emergence of the material being extruded, that is, its rate of flow through the orifice, is largely dependent upon the shape and "suits in an advanced rate of extrusion. On the other hand, as the curved surface adjacent the orifice is increased in angularityto provide a somewhat conical efiect there is a corresponding decrease in the rate of extrusion.

The die surface is reversely curved as hereafter set out to provide a major portion which is generally concave and merges with the die side walls. Merging with the orifice and with the concave portion is a generally convex section formed in the die face. It is this latter part which governs the rate of emergence.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means and steps hereinafter fully described and particularly pointed out in the claims; the annexed drawings and the following description setting forth in detail certain means and one mode of carrying out the invention, such disclosed means illustrating, however, but one of various ways in which the principle of the invention may be used.

In said annexed drawings- Figs 1 through '7 inclusive, show successive stages in the extrusion of a billet made up of alternate layers of light and dark material;

Fig. 8 shows the last step in extrusion as the final slug actually results in practice;

Figs. 9, 10, 11 and 12 each show the various positions of a respective layer of the material shown in Figs. 1 through 7, in which Fig. 9 corresponds to the 4th layer from the orifice face of the die; Fig. 10 corresponds with the 8th layer; Fig. 11 corresponds with the 12th layer; and Fig. 12 corresponds to the 18th layer;

Fig. 13 shows a composite die curve constructed from Figs. 9 to 12;

Figs. 14, 15, 16 and 17 show successive stages in an extrusion cycle embodying my invention;

Fig. 18 is a view of a ram and die constructed in accordance with my invention for extruding circular objects;

Fig. 19 (a, b, c, d. and e) show a longitudinal section through an extruded article extending from the crop end to where the flow lines become parallel;

Figs. 20, 21 and 22 are transverse sections showing modifications of rams employed with my invention; and

Fig. 23 is a transverse section through a compound orifice to be employed.

Briefly, my invention consists of guiding the material during extrusion by a confining shell formed of the slug itself in which the bulk of the material will pass through the orifice and a thin layer of material will remain in the die to form the shell. A die is provided to support the slug and also act as an outer supporting case for the theoretical shell above referred to. The configuration of the die is such that the theoretical shell is formed with a surface coinciding with the normal flow lines of the material under extrusion. This permits the use of a minimum amount of power, together with the obtaining of the desired physical characteristics in the extruded article.

The form to which this theoretical shell is to be held may be generally said to be defined by the angle of rupture of the material under extrusion. As a practical matter, however, the

shell assumes a somewhat different shape because of the variables introduced by the plasticity and viscosity of the material, which in turn are controlled by the temperature. Further factors are the ratio of reduction and the speed with which the ram travels.

Expressed in another way, the theoretical die shell is a lining covering the die proper and consists of a thin outer layer of the slug lying against the die which is replaced each time a new slug is supplied for the previous one.

It is of course apparent that in extrusion as heretofore practiced, part of the slug would remain stationary with respect to the die while another part would move. However, my invention is distinctly different for several reasons.

In the first place, the theoretical shell to which I refer is for practical purposes of negligible thickness and is so small a percentage of the entire slug that, as a practical matter, it may be said to be non-existent. Furthermore, this shell is oi. substantially uniform cross-sectional thickness at all points over its surface and is in no sense similar to the large tapered ring of material formed in the corner of the die as hereafter discussed in relation to Figs. 1 through 7.

Also, the theoretical shell is so shaped and established by the actual die that uniform, smooth flow is introduced at all points over its surface, which is sharply distinguished from the tearing action encountered when a slug is forced out of an orifice as has heretofore been done and is not guided out as contemplated by my invention.

In extrusion processes heretofore practiced the slug was torn by the ram to cause relative flow between the parts without regard to the normal fiow lines, while with my invention the slug is shaped by the die to position the material for extrusion along these flow lines.

Material undergoing extrusion desires to follow certain definite trends as shown in Figs. 1 through 7. Here I have shown a series of successive stages in the extrusion of a cylindrical slug made up of alternate layers of light and dark modeling clay. Each of the layers is of the same thickness and the different positions represent a half-inch advance of the ram; the slug being 6" in diameter.

The ram employed has a fiat face and the die in turn was cylindrical with a fiat face adjacent the orifice; no attempt being made to conform the parts to embody my invention. These figures illustrate the tendency of materials undergoing extrusion to assume natural fiow lines and, as hereafter pointed out, a die and ram designed in accordance wtih this tendency will result in a maximum eificiency of extrusion.

Referring to Fig. 1, it will be seen that during the first half-inch of extrusion the layers of material adjacent the ram have encountered practically no deformation, all of the deformation being accounted for in the first few layers adjacent the orifice and then only in that part of those layers at the center of the die. As the extrusion continues the die and ram shape cause compacting of the material and the layers close to the ram are increasingly affected until, in the extreme position, even the layer against the ram has partially passed through the orifice to take its place as the central section of the extruded article.

The deformation of the slug takes place in two major portions, namely, in the region along the die axis on the orifice side first and in the region close to the outer die side wall. This latter deformation begins near the orifice and continues toward the ram. This latter deformation becomes apparent in the layers close to the ram even in Fig. 1 and finally affects even those layers closest to the orifice.

By referring to Figs. 3 and 4, and particularly to the layer designated 20 thereon, it will be seen that for a considerable period of time during the extrusion this layer has been unaffected except at, its outer edges, but that finally, as shown in Fig. 4, it enters into the fiow zone and in a relatively short space of time moves with great rapidity out through the orifice to form part of the extruded article. An analogous situation is apparent in layer 20, as shown in Figs. 4 and 5. In Fig. 4 relatively little deformation of this layer has taken place, although in Fig. 5 the extrusion of the same layer is considerably advanced.

The ratio of reduction controls the speedof movement out of the flow zone. Thus, if the ratio is 16 to 1 the material leaves the zone at the orifice sixteen times as fast as it came into the zone..

The fiow zone is a central somewhat conical band of material within the slug and forms by the action of the ram. The least extrusion effect at a given instant is evident in the central part of the slug close to the ram and in an outer ring of the slug close to the orifice face of the die where the face merges with the side walls.

The material attempts to follow as extrusion progresses until, as best shown in Fig. 6, a sharply defined band consisting of several greatly thinned layers of material has been formed. Fig. 7 does not show this construction so well because here the extrusion has progressed so far that normal fiow had almost entirely ceased and the slug itself was directly compressed between the die face and the ram face without any appreciable part passing out of the orifice. Of course, if sufficient, pressure is applied the material can be forced out in spite of the compacting.

The position of any given layer during the extrusion cycle of Figs. 1 to 7 may be charted by outlining the location of a given layer during any part of the cycle. For purposes of illustration, the 4th, 8th, 12th and 18th layers, counting in a direction from the orifice toward the ram, have been plotted, as shown in Figs. 9, 10, 11 and 12respectively. From these figures it will be seen that the layers closest to the orifice have relatively little movement parallel to the axis and in effect move only to assume a position along the fiow curve and then remain substantially stable except as they are thinned out to provide material for the extruded article.

On the other hand, as shown in Fig. 10, all points of the 8th layer at first move substantially uniformly under the influence of the ram until the layer assumes a position corresponding to the natural fiow lines, after which the axial movement is relatively slight. 4

The same situation obtains with the 12th and 18th layers, as shown in Figs. 11 and 12, the extreme case of course being the 18th layer, which is against the ram. Here the movement, until the 5th position is reached, is such that the layer retains its wafer-shaped form. At the 5th position however, true, extrusion starts and continues, during which time the layer assumes a form finally represented by the 7th position, in which it too conforms to the flow lines of the material.

The composite result of the analysis just described is shown in Fig. 13 where the relative positions of each layer corresponding to the flow lines are plotted to provide a curve, as indicated concave with respect to the ram, changing into a relatively small convex area close to and intersecting with the orifice. This curve is formed by two arcuate portions merging in tangency at one part and at their ends meeting the orifice and die respectively, at the intersection with the orifice and die of a line at substantially 45 to the axis of the ram.

In general a die which conforms in contour to the curve 30 will produce the maximum extrusion efficiency with a minimum of power and at the same time obtain af strong extruded article with high physical characteristics well suited for handling severe stresses. This curve is modified as hereafter set out to meet various conditions. By providing such a die the slug will form itself to the contour and provide the theoretical shell above described. The die is so shaped that the shell will form with its inner face conforming to the fiow lines of the material under extrusion.

The die curve, as just described, is bounded at each end by a line lying at approximately 45 with the die side wall and the orifice edge. This line I call the median line. The angle of the line generally conforms to the angle of rupture of the material being extruded plus an allowance for speed of extrusion and the inherent molecular adhesion of the material. These latter features change the die from a true value corresponding vto the angle of rupture to the curves shown in Fig. 13. I

This angle of rupture for most materials capable of being extruded is between 42 and 48, and to this extent, subject to the modifying factors hereafter set out, may be said to critically define the most desirable die angles and vary the 45 figure above.

The material displaced and moved to and through the orifice at a given instant comes from a double convex area whose center line is the angle of rupture of the material. This zone conforms on one side to the desired form and accordingly the die is shaped to closely coincide with this configuration. On the other side, the zone as hereafter described determines the ram conour.

Abrasion in an ordinary extrusion die as heretofore used is extremely important and results in enormous wear as less plastic materials are-handled and I have found that with my invention abrasion is almost totally eliminated. This is due to the fact that the die surface is so shaped that the convex portion, looking toward the ram, extending from the die side wall toward the orifice terminates at the same point where; adhesion between the material and die ceases because 'at .this point flow of material transversely to the face is reversely curved, it will be seen (Fig. 13)

that the inner die surface is concaved inwardly as it leaves the die face and then adjacent the orifice proper is convexed. The first of these curves, which is the longer, is referred to as the power curve because it partially controls the power required and on proper design of the same, results in the use of a minimum amount of power to drive the ram. The major control of the power is obtained through the ram configuration,

as hereafter set out. The second curve will be referred to as the forming curve because the speed of emergence and elimination of abrasion is largely dependent on the form of this curve.

In obtaining the characteristics indicated and accomplishing the desired objects it has been found that these curves may be accurately laid out in accord with predetermined requirements, such as'will now be described. The first consideration in the proper design of the die is the amount of cross-sectional reduction which, once determined, gives the size of the die orifice in relation to the body diameter of the die. For purposes of illustration, assume that a 9 to 1 reduction is to be obtained and that the internal die diameter DI is three inches. Since the area of reduction varies as the square of the diamee ters, the orifice dimension D2 will be one inch. Since the orifice is in the center of the die this determines the location of the side walls of the same, as indicated by the point A. From the point A a line AB is drawn parallel to'the side walls of the die. From the point C a line is drawn lying at an angle of substantially between and to the line AB. From a point on the line AC, located as hereinafter explained, an arc of a circle AD is drawn.

The length of the arc AD, the angle of the line AC and the radius of the arc AD all control the speed of extrusion of the metal through the die. The greater the angle the more the speed of flow through the orifice is retarded. As the radius AC is increased the rate of extrusion is correspondingly decreased. Similarly, the longer the arc AD, the slower the rate of extrusion. The value of these factors is experimentally determined to produce the rate of flow required for the object to be extruded.

The angle of rupture of the material extruded determines the power curve and thus it may be said that the angle of rupture determines the scope of the confining die for the above discussed theoretical shell. This curve may be conveniently laid out in the following manner. Through the point A a line is drawn lying at an angle with the line AB corresponding to the angle of rupture of the material to be extruded. As heretofore stated, for most materials this angle lies between 42 and 48, and thus the line will be at such an angle with the ram axis since it is parallel to the line AB. The intersection be-' tween the line just mentioned and the die side wall, as at E, determines the beginning of the extrusion curvature. An arc of a circle is now drawn passing through the points D and E and tangentially connecting with the die side wall at E. The resultis the internal die configuration ADE. The curve may be somewhat flattened where it meets the side wall to provide additional space for receiving material from which the supporting theoretical shell is formed.

The die side wall below the point A is cut back as shown in Fig. 18. This is necessary to eliminate abrasion and is possible because the article extruded is completely formed by the curve ADE and after passing the point A need not touch any portions of the die.

A single orifice extrusion die constructed in accordance with these principles will result in uniform flow lines of the character above described and, insofar as is known, a uniformity in the extruded article unattainable with any form of extrusion die heretofore used.

Figs. 14, 15, 16 and 17 show successive stages in the extrusion of a cylindrical slug of clay made of alternate light and dark layers by means embodying my invention. By comparing these figures with Figs. 1 through '7 it will be immediately apparent that the ram and die configurations there shown, and which are made in accordance with the invention, promote a uniform flow of material over a theoretical shell 40. This shell is formed from part of the slug itself and is shaped by the configuration of the die wall. This is best illustrated in Fig. 17 by the wide dark colored section adjacent the die, which represents an inert part of the slug still substantially the same as the same layer 40 shown in Fig. 14 at the beginning of the extrusion.

Since all movement through the flow zone is bounded by part of the slug itself as above set out there is of course no abrasion in the backing portion of the die. The die'merely acts to reinforce and support the theoretical shell.

After a slug has been extruded the residual portion is removed, taking with it the portion 40, which is reformed as a new slug is placed in the die out of material composing the new slug.

Fig. 19, made up of parts a, b, c, d and c respectively, is in reality a single extruded section beginning with the crop end shown at the lower part of Fig. 19c and terminating with the upper part of Fig. 19a. It will be apparent from this figure that the article is composed of a series of shells, the sides of which finally become parallel as extrusion progresses. The only waste part of this material is a short crop end 42, which is out off and discarded because the material forming it has not become sufiiciently worked to-produce a desirable structure.

Referring back to Fig. 8, I have shown an actual cross-section of an extruded specimen made under actual practice conditions and attention is directed to this figure in connection with Figs. 14 through 17 above described. It will be noted that the flow zone is turbulent, as indicated at 45, which turbulence indicates irregular properties in the extruded article and-the requirement of considerably more force to overcome the turbulence in effecting extrusion. In this connection, Figs. 1 through 7 are far more ideal than obtained in actual practice because the material was allowed to come to rest each time it was sectioned to show the construction of one of the figures, and accordingly the turbulence effect has been greatly reduced. As a practical matter the 01d practice is indicated by Fig. 8 and not by the idealized Figures 1 through 7.

In general, the greater the arc of the concave portion of the die, looking from the ram, the

greater will be the speed of extrusion. I attribute this to the fact that the flow of material through the orifice corresponds with the angle of rupture of the material itself and the flow is the easiest when the angle of rupture is the greatest, or a straight line indicating no resistance to fiow. Tooth paste would be an extreme example of a material with no angle of rupture.

A compound die employing two or more orifices in the same die may be used, as shown in Fig. 23. The principles discussed in relation to a compound die apply irrespective of the number of reduction orifices. Each orifice of such a die is designed exactly as in the single die of Fig. 13.

The two dies cooperate however, due to one cardinal point in their construction, and this is that the angle lines AE of the outermost die must intersect a portion of the die side wall of the inner die formed in accordance with the line A E all as shown in Fig. 23. If this one point is observed there will be a true double extrusion.

assasoo If it is not observed the net result will be to compact the material in the comers of the die faces and provide an irregular single extrusion.

The ram employed in my invention is possessed of particular .characteristics not believed known before in extrusion rain construction. In genera], the ram slug engaging face is formed as a flat cone with the apex coinciding with the ram axis of movement and with the base of the cone behind the apex terminating adjacent the die side walls at the outer annular edge of the ram. Such a ram is shown in different forms in Figs. 20, 21 and 22.

Generally speaking, I have found that the most desirable ram results when the active face lies behind and is defined by an imaginary cone, the elements of which lie at an angle of substantially 30 to the ram axis for a reduction of 16 to l. The surface itself comprises a generally conical convex ring which is flattened .at the nose or apex, as hereafter described. The above angle increases as the reduction ratio increases and likewise decreases with the reductioriratio.

The ram is given the above shape to rapidly conform the material to the desired flow lines. Thus initially it should apply pressure at points to conform to these lines in order to promptly initiate proper flow in thearticle. For this reasonthe entire ram surface lies within the imaginary cone above described, the elements of which cone I have hereafter called the median lines of the ram.

The type of cross-section obtained in the finished article is controlled by the configuration of the ram. For instance, if the article is to withstand torsion and must be strongest at its outer surfaces it should be provided with a blunt nose, as shown in Fig. 22. By this construction the outer portions of the slug will be engaged and worked more thoroughly and hence the outer shell of the extruded article will likewise be more thoroughly worked.

"If the article is to be uniformly worked throughout the ram should have a configuration similar to that shown in Fig. 21, where the flattened portion represents a compromise between the blunt nose of Fig. 22 and the sharper nose of Fig. 20.

This latter construction is employed where the article is to be center worked, that is, with the more complete working through the region close to the articles central axis.

The convexly curved portion of each of the rams shown in Figs. 20 and 22 is formed along an arc of a circle which intersects the above described median line at the die side wall and at the ram axis. The flattened nose portion in turn merely represents a cutting down of the extreme length of the die working face. pressed in another way, this means that the nose curve and the convex side curves become tangent with each other at varying distances, such as K, L and M in Figs. 20, 21 and 22 respectively; depending on the degree of working to be given to the finished piece.

In transforming materials from their initial state to the final article it is frequently desirable to subject them to severe working in order that a desired grain structure and corresponding physical characteristics may be obtained at the end of the operation. For instance, in rolling materials they must be frequently reheated and annealed to prevent the formation of a brittle structure and in many cases they must be crossrclled at an angle transversely of the prior rollemployed of rolling and cross-rolling slabs.

With my process and with a single pass through an orifice I have obtained an ultimate strength of wrought iron of 57,000 pounds per square inch longitudinally and a transverse strength of 46,300

pounds per square inch, compared to standards of 48,000 pounds per square inch and 44,000 pounds per square inch respectively. Similarly, I have extruded nickel in one operation directly from the ingot and have obtained characteristics fully equivalent to those now commercially obtained by several stages of rolling.

From the foregoing description it will be seen I that my invention embodies a method and an apparatus which permits the extrusion of articles of uniform characteristics and without bending as the same leaves the orifice and that these results arise from a very much more efficient extrusion process than has heretofore been known.

Other forms may be employed embodying the features of my invention instead of the one herein explained, change being made as regards the means and the steps herein disclosed, provided the elements stated by any of the following claims or the equivalent of such stated elements be employed, whether produced by my preferred method or by others embodying steps equivalentto those stated in the following claims.

I therefore particularly point out and distinctly claim as my invention:

1. In a die for use with a ram for extruding material, side walls, a die face positioned for cooperation with a ram, said die face comprising a generally concave portion whose median lines intersect the die sidewalls at angles of substantially 45.

2. In a die for use with a ram for extruding material, side walls, a die face positioned for cooperation with a ram said die face comprising a generally concave portion whose median lines intersect the die side walls atangles of substantially 45", an orifice adjacent the mid-portion of said die face and positioned to be intersected at the orifice edge by said median lines extended.

3. In a die for use in a ram for extrudin material with a definable angle of rupture, side walls, a die face positioned for cooperation with a ram said die face comprising a generally curved portion whose median line intersects the die side walls at substantially the angle of rupture for the material under extrusion.

4. In a die for use in a ram for extruding material, side walls, a die facepositioned for cooperation with a ram said die'face comprising a generally curved portion whose median line intersects the die side walls at substantially the angle of rupture of the material, said die face having a concavity in the direction of extruding movement of the ram, said concavity being formed to correspond to the plasticity of the material under extrusion.

5. In an extrusion ram, a face adapted to engage and force material through an orifice comprising a generally convex face formed along a line intersecting the ram axis at an angle equivalent to the angle of rupture plus one-half of the angle of repose for the material being extruded.

6. In an extrusion ram, a face adapted to engage and force material through an orifice comprising a generally convex face formed along a median line intersecting the ram axis at an angle of approximately 30 thereto.

7. In apparatus for extruding plastic material through an orifice comprising a. die and ram with cooperating faces, said ram face having a generally concave material contacting surface with a partially flattened nose, and said die having a generally concave material contacting surface.

8. In apparatus for extruding plastic material through an orifice comprising a die and ram with cooperating faces, said ram face having a generally concave material contacting surface with a partially flattened nose and said die having a generally concave material contacting surface, said surface merging with the orifice in a reversely curved convex portion merging with said generally concave portion.

9. In an extrusion die, a straight side wall portion, a die end formed with an orifice therein and a die face connecting said orifice and said side walls and comprising a generally concave shape bounded at the orifice end and the side wall line by a cone whose elements intersect the side walls and a line parallel with the axis through the orifice edge at an angle of approximately 45.

10. In an extrusion die, a straight side wall portion, a die end formed with an orifice therein and a die face connecting said orifice and said die walls and comprising a generally concave shape bounded at the orifice end and the side wall line by a cone whose elements intersect the side walls and a line parallel with the axis through the orifice edge at the angle of rupture for the material being extruded.

11. In an extrusion die, side walls, a die face merging with the die side walls and terminating in an orifice, said die face being formed to be substantially coincident with the outer limits of the zone of flow of the material within the die.

12. In an extrusion die, side walls, a die face merging with the die side walls and terminating in an orifice, said die face being formed to be substantially coincident with and spaced from the outer limits of the zone of flow of the material within the die.

13. In an extrusion die, side walls, a die face merging with the die side walls and terminating in an orifice, said die face being formed to a curve bearing such relation to theangle of rupture of the material under extrusion that a shell of the material will be in fixed relation to the die face during extrusion and provide a guiding surface within the slug itself to form the material of the slug prior to emergence through the orifice.

14. In an extrusion die, side walls, a die face merging with the die side walls and terminating in an orifice, said die face being formed to a curve bearing such relation to the outer limits of the zone of fiow of the material under extrusion that a shell of the material will be in fixed relation to the die face 'during extrusion and provide a guiding surface within the slug itself to form the material of the slug prior to emergence through the orifice.

15. In apparatus for extruding plastic material through an orifice comprising a die and ram with cooperating faces, said die having a generally concave material contacting surface and said ram having a generally concave material contacting surface with a partially flattened nose, the curvature of said flattened nose being determined by the intended working of the slug during extrusion.

16. In apparatus for extruding plastic material throughan orifice comprising a die and ram with cooperating faces, said die having a generally concave material contacting surface and said ram having a generally concave material contacting surface with a partially flattened nose, said nose bing blunt in case the peripheral portions of the slug are intended to be worked more intensely during extrusion and said nose being sharper in case the central portion of the slug is intended to be worked more intensely during extrusion.

HARVEY M. GERSMAN. 

